1. Field of the Invention
The invention relates to an acceleration detector which detects acceleration generated by an impact of, for example, a vehicle collision and is utilized as a switch for activating a crash safety device such as an air bag of vehicles.
2. Description of Related Art
One of acceleration detector comprises a rotor which is rotatably supported within a housing and rotates according to acceleration, and a pair of contact terminals contacting with each other by rotation of the rotor at an inner end portion provided within the housing to be in an electrically connected state. An example of this type of detector is shown in Japanese Patent Laid-Open Publication No. Hei 11-174081.
In the acceleration detector shown in the above-mentioned publication, a rotor is rotatably assembled through a shaft, and a coil-like torsion spring urging the rotor to an initial position is assembled with a required gap to a cylindrical collar assembled on the shaft. Moreover, the inner end portion of the contact terminal is elastically and repulsively engaged with a cam portion provided to the rotor, and pressed and moved by rotation of the rotor against urging force of the torsion spring.
In the acceleration detector of the above-mentioned publication, the torsion spring which is supported by the collar installed on the shaft has disadvantages in terms of costs. In addition, since the spring effect center of the coil-like torsion spring and the rotary center of the rotor are displaced at least by the amount corresponding to the gap in the radial direction, the urging force to the rotor by the torsion spring may deviate from a desired value or design value, and a desired performance cannot be obtained. Moreover, edges at both sides of the inner end portions in the contact terminals may damage the cam portion when the rotor rotates at an engagement portion of the cam portion provided to the rotor and the inner end portion of the contact terminal, resulting in a risk that the desired performance cannot be obtained since the slide resistance between them is unstable.
It is an object of the invention to obtain the desired performance approximating the design value in an acceleration detector. According to a first aspect of the invention, the acceleration detector comprises a rotor rotatably supported within a housing and rotating against urging force of a torsion spring according to acceleration, a pair of contact terminals contacting with each other to be in an electrically connected state by rotation of the rotor at an inner end portion provided within the housing, and a supporting portion integrally formed with the rotor and supporting the torsion spring, the supporting portion being displaced by a predetermined amount in a predetermined direction from the rotary center of the rotor so that the spring effect center when torque is exerted on the torsion spring by rotation of the rotor substantially corresponds to the rotary center of the rotor.
The acceleration detector according to the first aspect of the invention enables reduction of the costs since the supporting portion is integrally formed with the rotor and supports the torsion spring. Moreover, the supporting portion is displaced by the predetermined amount in the predetermined direction from the rotary center of the rotor so that the spring effect center when torque is exerted on the torsion spring by the rotation of the rotor substantially corresponds to the rotary center of the rotor, whereby, the desired urging force, approximating the design value, of the torsion spring is applied to the rotating rotor to obtain the desired performance.
Moreover, the acceleration detector according to the second aspect of the invention comprising the rotor rotatably supported within the housing and rotating according to acceleration and a pair of the contact terminals being pressed by the cam portion rotating integrally with the rotor at the inner end portion provided within the housing and contacting to each other to be in an electrically connected state is characterized in that the width of the inner end portion of the contact terminals pressed and moved by the cam portion is formed larger than that of the cam portion and edges at both sides of the inner end portion of the contact terminals are arranged so as not to be engaged with the cam portion.
In the acceleration detector according to the second aspect of the invention, the width of the inner end portion of the contact terminals pressed and moved by the cam portion is formed larger than that of the cam portion, so that edges at both sides of the inner end portion of the contact terminals are arranged so as not to be engaged with the cam portion; therefore, when the rotor rotates, the edges at the both sides of the inner end portion in the contact terminals do not damage the cam portion in the engagement portion of the cam portion rotating integrally with the rotor and the inner end portion of the contact terminals and the slide resistance between them can be stabilized. Accordingly, the desired performance can be obtained.